Beyond the Root: Linking Economics Space, Symbiosis and Exudation in Phosphorus-Stressed Eucalyptus Species

Plant roots exhibit coordinated suites of functional traits that reflect different strategies for nutrient acquisition, commonly described along the root economics space (RES). In phosphorus (P)-limited systems, plants may rely on contrasting pathways for P acquisition, including fine-root proliferation, root exudation, and mycorrhizal symbioses. However, how these strategies are coordinated across genotypes within a single tree genus remains poorly understood.

Here, we investigate root economic traits, mycorrhizal colonization, and root-associated metabolites in twelve eucalypt species grown under controlled low-P conditions. We quantify key root morphological traits (e.g. root diameter, specific root length), mycorrhizal (AM and ECM) colonization, extraradical hyphal development, and the composition of root exudates, with a particular focus on organic acids and phenolic compounds.

Preliminary analyses indicate pronounced interspecific variation in root traits and associated P-acquisition strategies across eucalypt species. Trait coordination patterns suggest potential trade-offs between root morphological investment, symbiotic associations, and metabolic pathways involved in P mobilization. In particular, variation in root diameter appears to be associated with shifts in the relative reliance on root-based versus mycorrhiza-mediated strategies for P acquisition, although the strength and consistency of these relationships are still being evaluated.

Overall, this study aims to provide a trait-based framework for understanding how woody plant species coordinate alternative P-acquisition pathways under nutrient limitation. By integrating root economics, symbiotic interactions, and root metabolic traits, our work contributes to a more mechanistic understanding of belowground resource foraging strategies in forest ecosystems.